The invention relates to catalyst supports and like devices for use in treatment of fluids by interaction with a solid surface. The invention is particularly concerned with catalyst supports for catalyst systems required to withstand a severe environment and repeated thermal cycling such as is met by a car exhaust treatment system.
U.S. Pat. No. 3,920,583 describes a catalyst system comprising an aluminium bearing ferritic steel substrate, an electrically insulating ceramic layer on a surface of said ferritic steel substrate, and a catalytic material supported upon the ceramic layer, said aluminium bearing steel substrate comprising an alloy of iron, chromium, aluminium, and yttrium, and having the property of forming an alumina layer on heating in air, said alumina layer protecting the steel substrate against further oxidation attack, and said ceramic layer comprising a layer of alumina formed by heating the aluminium bearing ferritic steel substrate in the presence of oxygen to cause the formation of a layer of alumina on the surface of the ferritic steel substrate from aluminium within the ferritic steel substrate, thereby forming a tenaciously adherent ceramic layer on said ferritic steel substrate.
U.S. Pat. No. 3,920,583 describes a substrate formed from the alloy into a cylindrical matrix which may be in the form of a wire bundle or may be formed from 0.0125 cm thick sheet corrugated and wound up, with an interleaved plane sheet, into a spiral.